loop: only freeze the queue in __loop_clr_fd when needed

->release is only called after all outstanding I/O has completed, so only
freeze the queue when clearing the backing file of a live loop device.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Tested-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20220330052917.2566582-11-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>